JP-A-2000-250378 discloses an image formation apparatus, and a process unit including a developing cartridge and a photoconductor cartridge. The developing cartridge is detachably mounted to the photoconductor cartridge to form the process unit. The process unit is detachably mounted to the image formation apparatus.
More specifically, the developing cartridge has a developing roller and an operated section. The photoconductor cartridge has a photoconductor drum, a slide support member, and a move operation section. A housing of the image formation apparatus has a guide.
When the developing cartridge is mounted to the photoconductor cartridge, the developing roller is located close to the photoconductor drum and the operated section is located adjacent the slide support member. When the process unit is mounted to the apparatus housing, the move operation section comes in sliding contact with the guide to change the attitude of the slide support member. The slide support member correspondingly presses the operated section to press the developing roller against the photoconductor drum.
Because the image formation apparatus is required to apply a developing bias to the developing roller, an electrode is provided on the apparatus housing, so that when the process unit is mounted to the apparatus housing, the electrode is brought into contact with and electrically connected to a shaft of the developing roller to apply the developing bias to the developing roller.
On one hand, in order to keep the image quality, it is required to press the developing roller against the photoconductor drum uniformly in the axial direction. On the other hand, because vibrations occur due to rotation of the photoconductor drum during image formation, it is required to permit slight movement of the developing cartridge relative to the photoconductor cartridge to follow and absorb such vibrations. However, in a case in which the developing roller shaft and the apparatus housing electrode are contacted with each other to apply the developing bias to the developing roller, the slight movement of the developing cartridge relative to the photoconductor cartridge may result in an unstable contact between the developing roller shaft and the apparatus housing electrode, i.e. an unstable supply of the developing bias to the developing roller. In this connection, if contact pressure between the developing roller shaft and the apparatus housing electrode is increased in an attempt to make the contact therebetween stable, the developing cartridge cannot sufficiently follow vibrations caused by rotation of the photoconductor drum to undesirably degrade the image quality.